1. Field of the Invention
The present invention relates to a piezoelectric actuator, a method of manufacturing a liquid ejection head, a liquid ejection head and an image forming apparatus, and more particularly, to technology for manufacturing a liquid ejection head which ejects liquid from a nozzle and a structure of a liquid ejection head.
2. Description of the Related Art
An inkjet recording apparatus having a head (i.e., a liquid ejection head) is known in which the wall surface of a pressure chamber is deformed owing to displacement of a piezoelectric element and the ink inside the pressure chamber is pressurized, thereby causing an ink droplet to be ejected from a nozzle connected to the pressure chamber.
In recent years, since higher integration have been necessary in heads used in inkjet recording apparatuses, then various design modifications have been contrived in respect of the structure and manufacture of piezoelectric elements which generate the ejection force, in order to achieve high integration of heads and ensure high reliability and high performance.
Japanese Patent Application Publication No. 2001-152361 discloses the structure of a thick piezoceramic film formed by a gas deposition method. In this structure of a thick piezoceramic film, film formation based on the gas deposition method is carried out after forming an intermediate film on a substrate, thereby reducing the substrate damage and preventing reduction of the mechanical strength of the laminated structural body formed by the piezoceramic film and the substrate.
Japanese Patent Application Publication Nos. 2005-35013 and 2005-35018 disclose a method of manufacturing a liquid movement device in which a diaphragm is bonded to an ink storage chamber and a piezoelectric film is formed thereon and annealed, thereby producing a piezoelectric body having a thin film thickness. Thus, even if the piezoelectric body is driven at a low drive voltage, sufficient pressure is applied to the liquid inside the liquid chamber and the liquid can be moved to the exterior from the liquid chamber.
Japanese Patent application publication No. 2000-37877 discloses a method of manufacturing an actuator in which an oxidation resistant film (a metal oxide film) is formed on a diaphragm of a thin metal plate by the vacuum deposition method, prior to a calcination step of calcining a piezoelectric body at a high temperature, in order to prevent changes of properties and shape of the diaphragm in the calcination step.
However, in a case where an actuator (piezoelectric actuator) includes: a diaphragm (substrate) using metal containing iron (Fe) such as stainless steel; and a piezoelectric body (piezoelectric element) made of PZT (including Pb(Zr—Ti)O3 (i.e., lead titanate zirconate)), or the like, the iron contained in the diaphragm diffuses into the piezoelectric body owing to the high temperature (600° C. or higher) during deposition of the piezoelectric body or during the post-annealing process, and therefore it is difficult to satisfactorily obtain the required characteristics in the actuator. Moreover, from the viewpoint of preventing warpage of the diaphragm due to the heat treatment process, it is necessary to harmonize the coefficients of linear expansion of the diaphragm and the piezoelectric body.
In the invention disclosed in Japanese Patent Application Publication No. 2001-152361, an intermediate film made of SiO2, TiO2, ZrO2, or the like, is formed on the substrate (principally, a fragile material such as silicon), in order to prevent substrate damage or decline in mechanical strength during film deposition by a gas deposition method. However, the presence of an intermediate film of this kind is undesirable from the viewpoint of preventing warpage of the substrate, and moreover, it may cause manufacturing costs to increase. Furthermore, the thickness of the diaphragm is increased in dependence upon the film thickness of the intermediate film, and there is a possibility that the amount of displacement of the diaphragm declines.
In the inventions disclosed in Japanese Patent Application Publication Nos. 2005-35013 and 2005-35018, an annealing process is carried out for several hours in a high-temperature atmosphere of 600° C. to 750° C. (AD method: Aerosol Deposition method) or 600° C. to 1200° C. (sol gel method), and therefore, the iron contained in the stainless steel diaphragm diffuses into the piezoelectric elements and degrades the performance of the piezoelectric elements.
In the invention disclosed in Japanese Patent Application Publication No. 2000-37877, the oxidation resistant film (metal oxide film) formed on the diaphragm constituted by a thin metal plate does not have a minute structure, and hence it is difficult to prevent diffusion of iron contained in the diaphragm into the piezoelectric elements. Moreover, there is a possibility that the amount of displacement of the diaphragm is reduced owing to the thickness of the oxidation resistant film formed by the vacuum deposition method, and furthermore, it may cause manufacturing costs to increase.